This invention relates to apparatus for growing semiconductor crystals, such as, for example, silicon or germmanium crystals, by the Czochralski method, more particularly to apparatus for automatically controlling the diameter of such a crystal at all diameter values from seed to final taper while the crystal is being pulled, and it is an object of the invention to provide improved apparatus of this nature.
The Czochralski method of crystal growing is well known and various schemes are available in the prior art for controlling the diameter of the crystal to a single value during the crystal pulling, or growing, process. While such diameter control schemes have been of the closed loop variety, it has not been known to use a stationary optical system which encompasses, optically, the whole range of crystal diameters from seed to final taper and to automatically control the diameter at all values including the final value according to predetermined settings of these parameters. Accordingly it is a further object of the invention to provide an improved system for crystal diameter control of the nature indicated.
It is a further object of the invention to provide an improved crystal diameter control of the character indicated which is simple in form, accurate in operation and achieves higher quality crystals, for example, crystals having better thermal stability and more consistent and repeatable crystal diameter.